The following invention relates generally to an instrumentality for pulling cable which is to be preferably installed either in an overhead or underground environment and includes replacing existing cable.
The art of pulling cable in either an underground or an overhead environment has traditionally required the use of different mechanisms since the angle of attack for each job imposed loads upon the pulling apparatus which would be too diverse for a single pulling device. Since the winch mechanism associated with the pulling instrumentality has traditionally been mechanical or hydraulic, binding of the cable or awkward angles of attack can cause nonconstant hydraulic loading to the detriment of the pulling mechanism. In addition, the cable drum upon which the cable is to be wound and unwound reflects a change in effective diameter as the cable is being wrapped/unwrapped thereover providing a different moment arm in the rotation of the drum which must be compensated for in the hydraulic control device both when taking cable up and paying cable out.
Various attempts in the prior art have been chronicled which purport to address themselves to one or a plurality of the above noted problems in designing a pulling mechanism and attempts in the known prior art have taken the following courses: the design of two distinct machines to effect pulling from an overhead or an underground environment; the provision of a friction disc to control the winding and unwinding rate and tension of cable upon an associated drum, and various instrumentalities to override the effect of cable binding, build-up or dissipation on an associated drum which in and of itself alters the moment arm and pull rate, the effect of which has been offset in the past by pressure relief solenoid control valves or clutch mechanisms.
The following citations reflect the state of the art of which applicant is aware insofar as they appear to be germane to the process at hand. U.S. Pat. Nos. 3,226,088, Habighorst, Dec. 28, 1965; 3,448,962, Miller, June 10, 1969; 3,544,070, Blume, Dec. 1, 1970; 3,968,952, Newell, July 13, 1976; and 4.026,483, Skalleberg, May 31, 1977.
Publications Holan Brochure-page G-9 Braden Constant Load Winch Brochure-page 11-7294-1 Gear Products Inc. Brochure- "Planetary Winch" Morse -Page A-180 "Torque Limiter"
The Holan swivel sheave provides a support structure adapted to be disposed upon the trailing portion of a vehicle bed that includes an upwardly extending swivel and housing having a plurality of ball bearings interposed therebetween and an outwardly extending pulley sheave in which a sheave support arm is capable of articulation within a 360.degree. range so that cable can address a winding drum from a substantially constant direction. It should be clear that the outwardly extending support arm provides a bending moment on the swivel housing support and ball bearing structure fastened to the trailing portion of the truck bed and provides a pressure gradient on the ball bearings as well as providing other difficulties. More specifically, most cable pulling apparatus include a hook integrally formed with the associated cable which must be passed over the rotatable sheave and the Holan sheave requires removal of the hook assembly from the cable to allow the cable to be threaded over the sheave in contrast to the instant invention. That is to say, the instant invention distinguishes itself over this known prior art in its ability to provide a swivel support which is readily disassociated from its associated mounting bracket whereby a cable and its associated hooked end can be looped over the swivel sheave without removal of the hook from the associated cable and that there is a beneficial force distribution. Moreover, Holan's required small diameter sheave and its associated severe curvature will deformably and permanently stretch outer strands of the cable during typical loads so that the cable will no longer be straight but will be coiled like a spring.
The Braden publication provides a winch adapted to operate under a constant load environment and requires the use of a friction clutch to act as a drum brake for providing the constant load necessary in pulling endeavors of this sort. A cable path is provided which attempts to negate the effect of cable build-up on an associated drum, and as shown in FIG. 3 of the publication, an operator is required to attend the friction drive portion of the storage drum to alter the change in pulling forces as a function of cable build-up, cable pay out, or wear in the friction clutch assembly, resulting in a somewhat labor intensive product.
The instant invention is distinguished over the known prior art in that hydraulic relief is provided in such a manner that compensation for cable winding build-up is automatically offset not only when the cable is being wound on a drum, but also when it is being unwound so that the hydraulic valve arrangement provides an automatic resistance of braking effect when paying out cable. It is of utmost importance that the winding rate be constant and that the force exerted through the cable be constant so that inordinate pay out or take up rates do not occur.
The patent to Habighorst teaches the use of pulling cable through an underground conduit; the patent to Skalleberg provides an overhead support similar to Habighorst and the remaining citations show the state of the art further and are believed to diverge even more than that which is defined as the invention in the instant application.
The Gear Products winch constitutes a component which, when modified in a novel manner, evolves into applicant's bull wheel.